This invention relates to radio direction finder (df) apparatus, and more particularly to antenna apparatus for use with df receiver radios.
Radio direction finders measure the direction of arrival of a given radio signal. Typical direction finder systems are comprised of an antenna for detecting the desired wave signal, receiver means to limit the signal bandwidth, a processor to interpret the significance of the detected signal and output means for making use of the processed information.
A radio signal is actually a traveling wave that radiates outward from its exciter. The phase progression of the radio signal is the fundamental characteristic used by df systems to provide location information of the source of the wave. Typical df antennas are comprised of a plurality of elements and operate by determining the angle of arrival (azimuth) of a respective wave signal, thereby providing phase difference data necessary to determine df characteristics. Multiband df antenna typically cover frequency ranges of 20 to 1200 MHz. In order to avoid interaction of closely spaced antenna elements, each band of a multiband df antenna normally resides in its own plane. Although this "stacked wedding cake" approach provides nominal radio operation, the physical dimensions are often burdensome or unacceptable for certain applications.
Accordingly, a need exists for a df multiband antenna apparatus in which the low frequency band antenna elements define the required dimensions of the antenna.